With rapid development of wireless communications, MIMO technology has aroused interest because of its possible applications in digital television (DTV), wireless local area networks (WLANs), metropolitan area networks (MANs), and mobile communications. In brief, MIMO is an antenna technology for wireless communications in which multiple antennas are used at both the source (i.e., transmitter) and the destination (i.e., receiver).
In MIMO wireless networks, a general resolution for improving performance of systems with limited transmission power and/or with long distance between the destination and the source is adopting a relay-assisted transmission. Furthermore, the relay-assisted transmission associated with an amplify-forwarding architecture which receives a signal from the source and forward to the destination after amplifying is a popular choice in the present relay technique for easier implementation.
Based on the amplify-forwarding architecture, using a single-antenna distributed configuration at least comprise the advantages of higher flexibility and spatial diversity so as to be easily and effectively designed. However, conventional relay-assisted transmissions having the single-antenna distributed configuration for use in a MIMO system faces the difficulty in efficiently optimizing the relay gains for capacity improvement. The major reason is that a necessary matrix determinant for the capacity calculation can not be readily resolved by conventional beamforming or matrix decomposition techniques.
In view of this, since no useful resolution to deal with the problem up to now, an urgent need exists in the art to effectively overcome the shortcomings of conventional relay-assisted transmissions having the single-antenna distributed configuration for use in a MIMO system.